Year : 2009 | Volume
: 52 | Issue : 2 | Page : 215--216
Diffuse lipomatosis of the thyroid gland: A pathologic curiosity
Ruchika Gupta, Raman Arora, Alok Sharma, Amit Kumar Dinda
Department of Pathology, All India Institute of Medical Sciences, New Delhi, India
162, Pocket-B, Sarita Vihar, New Delhi - 110 076
We report the case of a 45-year-old man who presented with a 4-year history of midline neck swelling associated with recent onset respiratory distress. Local examination showed a lobulated diffuse thyroid enlargement. A subtotal thyroidectomy was performed. The right lobe weighed 225 g and the left lobe weighed 130 g. Multiple sections from both the lobes revealed diffuse infiltration of the stroma by mature adipose tissue. There was no evidence of amyloid deposits or papillary carcinoma. A final diagnosis of diffuse lipomatosis of the thyroid gland was rendered. Lipomatosis or adenolipomatosis of the thyroid gland is an extremely rare entity. The various differential diagnoses of fat in the thyroid include benign entities like amyloid goiter, adenolipoma, lymphocytic thyroiditis, intrathyroid thymic or parathyroid lipoma and malignant tumors like liposarcoma and encapsulated papillary carcinoma. Adequate clinical details and a thorough histopathological examination are mandatory for diagnosis.
|How to cite this article:|
Gupta R, Arora R, Sharma A, Dinda AK. Diffuse lipomatosis of the thyroid gland: A pathologic curiosity.Indian J Pathol Microbiol 2009;52:215-216
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Gupta R, Arora R, Sharma A, Dinda AK. Diffuse lipomatosis of the thyroid gland: A pathologic curiosity. Indian J Pathol Microbiol [serial online] 2009 [cited 2022 Jul 7 ];52:215-216
Available from: https://www.ijpmonline.org/text.asp?2009/52/2/215/48922
Infiltration of adipose tissue in the thyroid gland is uncommon. Such a phenomenon has been reported in heterotopic adipocyte nests, adenolipoma, amyloid goiter, lymphocytic thyroiditis, intrathyroid thymic or parathyroid lipoma, lipomatosis or adenolipomatosis, encapsulated papillary carcinoma and liposarcoma.  A close correlation between clinical features and histopathological findings is required to make the correct diagnosis, which is essential because the differential diagnosis also includes malignant tumors.
We report a rare case of a diffuse lipomatosis of the thyroid gland in a middle-aged man presenting with respiratory distress. A brief discussion on the various differential diagnoses is included.
A 45-year-old man presented with a history of a gradually enlarging midline neck swelling for the past 4 years. He had noticed a rapid increase in the swelling associated with respiratory difficulty for the past 6 months. However, there was no history of difficulty in swallowing or change in voice. On examination, a large lobulated thyroid enlargement involving both right and left lobes was noted. The lower end of the swelling was palpable. There were no signs of hypothyroidism or hyperthyroidism. Thyroid function tests were within reference ranges. A contrast-enhanced computed tomography scan showed an enlargement of the thyroid reaching inferiorly till the suprasternal notch and compressing the trachea. No retrosternal extension of the thyroid was noted. A subtotal thyroidectomy was performed and the specimen was submitted for histopathological examination.
We received the right lobe, left lobe, isthmus and pyramidal lobes separately. The right lobe measured 9cm × 7cm × 4cm and weighed 225g, the left lobe measured 9cm × 5cm × 3.5cm and weighed 130g, the pyramidal lobe measured 4cm × 3cm × 2cm and the isthmus was 2cm × 1.5cm × 1cm in size. A cut-section of all the specimens was similar and showed soft pinkish and grey areas with scattered yellow foci [Figure 1]. No focal lesion was identified in any of the specimens. Multiple histological sections from all specimens revealed similar morphology consisting of colloid-filled thyroid follicles lined by cuboidal cells and showing minimal variation in size. The interfollicular stroma showed infiltration by mature adipose tissue [Figure 2]. No lymphocytic infiltrate, follicular destruction or amyloid deposition was noted. There was no focus of papillary carcinoma in the sections examined. A diagnosis of diffuse lipomatosis of the thyroid gland was rendered.
Presence of adipose tissue in the thyroid gland is an infrequent phenomenon, unlike parathyroid, thymus, salivary gland or pancreas. In the normal thyroid gland, few adipocytes may be found near the capsule and in the perivascular location.  The various differential diagnoses of the presence of mature adipose tissue in the thyroid, like in the present case, include heterotopic nests of adipocytes, diffuse lipomatosis or adenolipomatosis, adenolipoma (thyrolipoma), amyloid goiter, lymphocytic thyroiditis, intrathyroid thymic or parathyroid lipoma, encapsulated papillary carcinoma and liposarcoma.  Heterotopic nests occur due to inclusion of fat cells in the thyroid before the formation of capsule. This is manifested by the presence of occasional small islands of adipose tissue, which are often detected incidentally.  The present case, in contrast, showed diffuse infiltration of the adipose tissue throughout the thyroid. Adenolipoma of the thyroid has also been named thyrolipoma or thyroid hamartoma and is an encapsulated tumor composed of a variable proportion of thyroid glandular tissue and fat.  The gross composition of fat may vary from 10 to 90% and hence the detection of adipose tissue on imaging also varies.  Our case did not show any mass lesion on gross inspection and, hence, this diagnosis was not considered. Lipomatosis, also called "choristomatous adiposity," demonstrates diffuse fatty infiltration rather than a single nodule.  Lipomatosis or adenolipomatosis may also manifest as a congenital swelling, as described by Simard and cited by Chesky.  Aspiration cytology of such lesions may yield a mixture of follicular cells and adipocytes and lead to a pre-operative diagnosis of fat-containing lesion of the thyroid.  The present case was not associated with lipoma at any other site and was not congenital in nature.
Adipose tissue infiltration has been reported in the thyroid gland with amyloid deposition in association with systemic amyloidosis. , No amyloid deposition was detected in the present case. Lymphocytic thyroiditis, a diffuse inflammatory process, may also be associated with fat infiltration. Liposarcoma of the thyroid gland is rare and presents with a rapidly growing mass with an aggressive clinical course. The long clinical course in the present case ruled out the diagnosis of liposarcoma. However, the recent increase in size and respiratory difficulty was worrisome for the clinician and prompted surgery. Because of the diffuse nature of fat infiltration and admixture of thyroid follicles, the possibility of intrathyroid thymic or parathyroid lipoma was not considered. Hence, the clinical and histological features suggested a diagnosis of lipomatosis of the thyroid gland.
The pathophysiology of adipose tissue infiltration in the thyroid gland is not clear and several theories have been proposed. Some authors consider this as a developmental anomaly, which can explain the heterotopic nests.  Others regard the presence of adipose tissue as a metaplastic process resulting from vascular changes with local hypoxia.  This explains the occurrence of fat in the amyloid goiter. Finally, one group of authors believes that fat in thyroid tumors is an integral neoplastic component of the tumor. 
The presence of macroscopic fat within the thyroid gland is rare, with few diagnostic possibilities. Most of these lesions are benign with the exception of liposarcoma and encapsulated papillary carcinoma. Because the differential diagnosis includes malignant entities, an accurate diagnosis is essential.
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